Bacon has been called the gateway meat, luring vegetarians back to meat. And hot dogs are a staple at many a backyard BBQ.

But a new study published in the Archives of Internal Medicine finds that daily consumption of red meat — particularly processed meat — may be riskier than carnivores realize.

"The statistics are staggering," study author Frank Hu, a professor of nutrition and epidemiology at the Harvard School of Public health, told us. "The increased risk is really substantial."

He found that people who consumed about one serving of red meat (beef, pork or lamb) per day had a 13 percent increased risk of mortality, compared with those who were eating very little meat. And processed meats raised the risk higher, to about a 20 percent increased risk of death from diseases including cancer and heart disease.

So the question lots of meat-lovers may ask is this: What amount of red meat can we consume if we don't want to increase our risks of these diseases?

"We're not talking about a vegetarian diet " says Hu. "A moderate consumption, for example one serving every other day, I think is fine."

And the American Cancer Society has a similar take. "Limiting [red meat] consumption to two to three times per week would be wise," says Marji McCullough, strategic director for nutritional epidemiology at the American Cancer Society.

The study found that people who replaced one serving of red meat with alternative sources of protein decreased their risks of premature death. Choosing chicken and other poultry decreased the risk by 14 percent, fish decreased the risks by 7 percent and legumes decreased the risk by 10 percent.

And what to do about bacon, sausages and other processed meats? Researchers advise cutting them back to a "once in a while" food. And lots of consumers have started looking for options with minimal processing, such as bacon without added nitrites.

McCullough says it's not clear why processed meats appear to be riskier. One theory is that the iron in meat works as a catalyst — to turn nitrites added as preservatives — into a particular kind of carcinogen in the body.

It's also possible that grilling the meat on a open flame explains part of the increased risk. "You're not only getting the nitrites, but you're also getting possible formation of carcinogens by cooking at high-heat temperatures or in direct contact with a flame" says McCullough.

The American Meat Institute Foundation disputes the findings that red meats including processed meats elevate the risk of cancer.

"I don't think there are a lot of risks associated with those processes [used to produce hot dogs or bacon]," says Betsy Booren, director of scientific affairs for the AMI Foundation.

"They're made from meat, which is needed in the body," Booren says. And she argues it's unfair to single out meat, when there are many risk factors for cancer and heart disease.

"It's your genetics and obesity. And it's overconsuming all foods, not just meat products" says Booren.

So maybe the meat scientists and the Harvard researchers do have something in common: Though they clearly disagree on risks, both seem to making the case for moderation.

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

Transcript

AUDIE CORNISH, HOST:

Bacon has been called the gateway meat for its powers to lure vegetarians back to carnivorous habits. And who among us - at least, the carnivores - has not devoured a hotdog at a backyard barbeque? Well, a new study may scare you away from the grill. It comes from the Harvard School of Public Health, and it finds that people who eat lots of red meat has significantly higher risks of cancer, heart disease and premature death. NPR's Allison Aubrey has the story.

ALLISON AUBREY, BYLINE: If you're a meat lover, I promise the news is not as bad it may sound. Nowhere in the story is anyone going to tell you that you must become a vegetarian. But if you consume red meat daily, as most of the volunteers in the study did - maybe bacon for breakfast and a burger for dinner - there's overwhelming consensus among nutrition researchers, including Margie McCullough, that this is too much.

MARGIE MCCULLOUGH: That's right. Absolutely, that would be considered too much. The evidence is convincing that red meat increases the risk of cancer.

AUBREY: McCullough is an epidemiologist with the American Cancer Society and she says the new study published today in the Archives of Internal Medicine adds to the evidence about how much risk comes with two servings or seven to eight ounces of red meat daily.

MCCULLOUGH: It's associated with approximately 40 percent increased risk of colorectal cancer and, as this study shows, about a 30 percent increased risk of death.

AUBREY: Now, we all have to eat something and we all end up dying, eventually, so lots of us want to know: is there a safe amount of red meat to consume if we don't want to add to our risks of these diseases? Frank Hu of the Harvard School of Public Health, who is the author of the new study, says he thinks so.

FRANK HU: Yeah. We are not talking about a vegetarian diet.

AUBREY: Who explains, based on his findings, he thinks that a half serving a day or, put another way, two to three servings a week, is what meat eaters could feel comfortable with.

HU: A moderate consumption, for example, one serving every other day, I think is fine.

AUBREY: Now, Hu changes his tune when it comes to processed meats, particularly hot dogs and bacon. These meats, he says, he's gotten completely out of his diet because his study and others suggest that they elevate the risks of cancer above and beyond that of unprocessed red meats.

HU: I mean, as a researcher, I always practice what I preach.

AUBREY: It's not clear why processed meats appear to be riskier. One theory is that the iron in meat works as a catalyst to turn nitrites, which are added preservatives, into a particular kind of carcinogen in the body. It's also possible that because hot dogs are often grilled, the direct access to the flame could be an issue.

Either way, the American Meat Institute Foundation disagrees with the findings that processed meats elevate the risk of cancer.

BETSY BOOREN: I don't think there are a lot of risks associated with those processes. First of all, they're all made from meat, which is needed in the body.

AUBREY: Betsey Booren is director of scientific affairs for the American Meat Institute Foundation. She says, after reviewing the new paper from the Harvard researchers, she finds it to be flawed in both its methodology and its conclusions. She points out that the findings come from analyzing food frequency questionnaires, basically surveys, asking volunteers to recall what they ate and then researchers keep track of the volunteers over decades to see if they develop particular diseases. It's not a very precise method and researchers have long acknowledged this, but it's long been considered the best way to pick up associations between diet and disease.

Booren says, given this methodology, it's unfair to single out meat when there are so many other factors that increase the risk of heart disease and cancer.

BOOREN: It's not one factor that raises your risk for disease. It could be your genetics and obesity and it's over-consuming all foods, not just meat products.

AUBREY: So maybe the meat scientists and the Harvard researchers do have something in common. Though they clearly disagree on risks, both seem to be making the case for moderation.